1. Field of the Invention
The present invention relates to an electron beam apparatus and its driving method, and more particularly to an electron beam apparatus and its driving method for applying the electron beam onto a target plane with the action of an electrostatic lens of an electrode having a feature of accelerating the electron beam.
2. Related Background Art
Along with the miniaturization of semiconductor devices, an electron beam exposure method has been used as means for forming minute patterns.
The accelerating voltage of the electron beam in the electron beam exposure method is increasingly important particularly in a range of several to several tens kV, due to the resolution and sensitivity of sensitive thin film (resist). With the progress of miniaturization of semiconductor devices, the process dimensions of 4 magabit DRAM and the following devices have become submicron, so that the diameter of the electron beam in an electron beam exposure apparatus is also required to be submicron.
On the other hand, the study of an electron source has been developed, whereby various types of elements have been proposed other than an electron emission element using a conventional hot cathode. For example, there have been proposed a type in which the reverse bias voltage is applied to a PN junction to cause the avalanche breakdown phenomenon so that electrons are emitted out of a element, as disclosed in Japanese Patent Application Laid-Open No. 54-111272 (corresponding to U.S. Pat. No. 4259678) and No. 56-15529 (corresponding to U.S. Pat. No. 4303930), a type in which the reverse bias voltage is applied to a Schottky barrier junction to cause the avalanche breakdown phenomenon so that electrons are emitted out of element, as described in Inst. Phys. Conf. Ser. No. 99, pp. 65 to 68, 1989, a type (MIM type) having a metal-insulator layer-metal configuration in which voltage is applied across two metal layers to cause the tunnel effect so that electrons passing through an insulator layer are emitted through a metal layer out of element, a surface conductive type (SCE type) in which voltage is applied to a highly resistive thin film in a direction orthogonal to the direction of film thickness so that electrons are emitted from a surface of the thin film out of element, a field effect type (FE type) in which the voltage is applied to a metal shaped to easily bring about the electric field concentration to develop locally an electric field of high density so that electrons are emitted from the metal out of element, a type in which a work function decreasing material layer is formed on a p-type semiconductive layer, and electrons are emitted by using the NEA (negative electron affinity) state whose vacuum level is at an energy level lower than the conduction band of P-type semiconductor, and other types.
Among these electron sources, four electron sources of the element in which the reverse bias voltage is applied to the PN junction to develop the avalanche breakdown phenomenon, the element in which the reverse bias voltage is applied to the Schottky barrier junction to cause the avalanche breakdown phenomenon, the MIM type element and the element using the NEA state have features that the electron beam obtained is superior in the parallelism, and they can be fabricated in minute area with the semiconductor process technique.
By the way, to meet the previously-mentioned requirement for the electron beam exposure apparatus, i.e., the requirement that the diameter of a beam spot on a target plane is submicron in a range of several to several tens kV of acceleration voltage, several stages of electromagnetic lenses as shown in FIG. 1 are used in a conventional apparatus.
An electron beam apparatus as shown in FIG. 1 is constituted such that the electron beam 111 emitted from an electron gun 101 is passed through electromagnetic lenses 102 having multiple stages for converging it to a desired spot diameter, a blanking electrode 103 for turning it on/off, and a deflection electrode 104 for deflecting it, before being applied on a target 110 placed on a table 108. In order to apply the electron beam 111 to a correct position of the target 110 placed on the table 108, it is constituted to measure the position with a laser interference meter 105 and move the target 110 to a desired position with a motor 107 based on the measurement. The target 110 is conveyed into or out of the electron beam apparatus by an automatic feeder 106. And to apply the electron beam precisely and correctly, they are disposed on an antivibration base 109 to prevent an adverse effect due to external vibrations.
However, there are following problems associated with the electron beam apparatus having several stages of electromagnetic lenses as above described.
(1) There are many components so that the apparatus is expensive.
(2) There are many components so that the apparatus including the antivibration base is heavy.
(3) There are many components so that the space volume occupied by the apparatus is large. Particularly, the apparatus is high (or long), and there are many racks storing control and power supply units.
(4) There are many components, therefore many adjusting portions, so that the adjustment for the performance of apparatus is complex and difficult.
(5) There are many components, thus many elements causing abnormality, so that the apparatus has a higher probability of failure and may lack in a sufficient reliability.
As electrons emitted from the electron gun usually used are divergent, it was required to use multiple stages of electromagnetic lenses to make the electrons a converged beam, particularly apply them onto the target in the order of submicron.
However, the finally converged electron beam is not obtained from all the electrons emitted from the electron gun, and was not sufficient from the viewpoint of the efficiency.